In color photography development it is necessary at an appropriate stage to remove the silver image, which, if left behind, would darken the dye image. Also it is necessary to remove unused silver halide because it darkens on exposure to light.
To remove the silver it has been previously proposed to convert it to silver halide with a suitable oxidizing agent known in the art as a bleach such as potassium ferricyanide or ferric iron complexed with ethylene diamine tetraacetic acid acting in the presence of potassium bromide. Alternatively, it has been proposed to use hydrogen peroxide as the bleach. The bleaching action of the peroxide is catalyzed by silver. Such a bleach has been described in U.S. Pat. No. 4,277,556 and has been referred to in the art as being of the "solvent type" because the silver is taken directly into solution and not converted to halide.
Under the action of a solvent bleach, soluble silver ions are formed and washed out of the photographic material and, as a result, build up in the bleach solution. This means that with solvent bleaches there is a risk of increased carryover of silver to the next stage of the process. Silver ions are environmentally undesirable. In order to minimize any silver being discharged, the silver ion concentration in the bleach should be kept low. This is usually achieved by adding replenisher at a rate to keep any carryover low. However this replenisher displaces silver-containing solution and the displaced solution must be desilvered in some way off line.
This problem has been solved by the present invention by removing at least part of the excess silver as an insoluble compound, for example, by adding a halide. The excess silver is the difference between the amount of silver actually in the solution and the amount necessary to catalyze the bleach action.